50 NATURAL SCIENCE [July 



The observations of Wesenberg-Lund (33) on the Eotifera of 

 Denmark, lead him to adopt Nnssbaum's view that nutrition is the 

 determining factor in the production of males. The chief result of 

 his researches is to show that, immediately before the normal period 

 of sexual reproduction, a period of very rapid parthenogenetic multipli- 

 cation sets in, and it is when this has reached its height that males 

 appear. Whenever it was seen that any one species was becoming 

 predominant in the gatherings from one particular source, the ap- 

 proach of the sexual period for that species could be predicted. He 

 finds, however, that, with the same species of rotifer, the sexual 

 period may occur at different times even in neighbouring ponds. 

 Lauterborn, on the other hand, states that the appearance of males 

 of the same species in very different localities, from lakes to puddles, 

 was often striking in its simultaneity. 



Though only indirectly connected with the present subject, we 

 may call attention in closing to some of the unexplained anomalies 

 in the distribution of the Rotifera. While the great majority are 

 notoriously sporadic and uncertain in their occurrence in any one 

 locality, yet Lauterborn and others have recorded cases where the 

 same species has appeared year after year in the same pool while 

 absent from all the surrounding localities. Very many species seem 

 to have a literally world-wide distribution, and their number is con- 

 stantly being increased ; yet there are instances of curiously re- 

 stricted range, and this in cases where insufficient search cannot be 

 adduced to explain their absence from certain areas. Thus Lacinularia 

 is common in many localities in England ; it swarms in every lough 

 in certain districts in the west of Ireland, appearing in July, as Mr 

 Hood (24) says, " as precisely to its season as the lapwing or the 

 swallow," and yet we are assured by the same excellent authority 

 that it is entirely absent from Scotland. Until 1883 the same 

 appeared to be the case with Stcphanoceros ; since then, Mr Hood tells 

 us, he has traced the gradual extension of its range until it has 

 become by no means rare in the lochs of Forfarshire and Perthshire. 



W. T. Calman. 



University College, Dundee. 



LITERATURE REFERRED TO 



1. Ehrenberg, C. G. — " Die Infusionsthierchen, u.s.vv." Fol. Leipzig, 1838. 



2. Kolliker, A. — " Furchungen und Saamenfaden bei einem Raderthiere." Froricp's 



Neiic Notizcn, xxviii., 16-20. October 1843. 



3. Brightwell, T. — :< Some account of a dioecious Rotifer allied to the genus Notommata 



of Ehrenberg." Ann. Mag. Nat. Hist. (2) ii., 153-158, pi. vi. Sept. 1848. 



4. Dalrymple, J. — " Description of an Infusory animalcule allied to the genus Notom- 



mata of Ehrenberg, hitherto undescribed." Phil. Trans., cxxxix. (1), pp. 331- 

 348, pis. xxxiii. and xxxiv. 1849. 



5. Huxley, T. H. — " Lacinularia socialis. A contribution to the Anatomy and 



Physiology of the Rotifera." Trans. Micr. Soc. London, (N.S.), i., 1-19, pis. 

 i.-iii. 1853. 



6. Conn, F. — " Ueber die Fortpflanzung der Raderthiere." Zeitsclir. Wiss. Zool., vii., 



431-486, pis. xxiii., xxiv. Dec. 31, 1855. 



